PROJECT SUMMARY: Interpersonal violence (IV) affects more than 1 in 5 young children in the United States annually. For young children, IV exposure most commonly occurs within the family context in the forms of partner violence and harsh/abusive parenting. Children exposed to IV represent a heterogeneous group. A portion of children develop psychological problems that cut across multiple diagnostic categories characterized by fear and distress symptoms. Existing models broadly implicate disruptions in biological stress systems in the etiology of violence-associated symptoms, but lack specificity for explaining heterogeneous symptom presentations in young children. Advancing this science requires novel laboratory and analytic methods for assessing and synthesizing threat reactivity across multiple biobehavioral levels. Inspired by the Research Domain Criteria (RDoC) initiative, we propose to achieve this by leveraging person-centered methods to identify unique profiles of threat reactivity across multiple levels of biobehavioral functioning never before studied together in young children: observed behavior, attention bias, autonomic reactivity, startle, event-related brain potentials. The fundamental scientific premise of the proposed work is that threat reactivity is a central intermediate phenotype linking early IV to this clinical vulnerability in young children. The proposed sample will include 360 children, ages 4 to 6 years, with (n = 240) and without (n = 120) IV exposure followed over 1 year. We advance three aims. Aim 1 is to map biobehavioral threat reactivity profiles to dimensional patterns of fear and distress in IV exposed and non-exposed young children. We hypothesize that we will identify hyper- and hypo-reactive profiles that link to greater symptoms relative to a non-extreme profile, and that hyper-reactivity will relate to fear, whereas hypo-reactivity will relate to distress at baseline and over 1 year. Aim 2 is to test whether threat reactivity profiles serve as intermediate phenotypes in explaining the link between violence exposure and symptoms over time. We hypothesize that children exposed to more severe IV will more likely be classified as hyper- or hypo-reactive and that profile type will mediate the link between IV and symptoms at baseline and 1 year later. Further, given high dependency of young children?s self-regulation on caregiving relationships and threats to regulatory capacity in violent environments, we hypothesize that mothers? ability to co-regulate their children?s negative affect will shape these risk pathways. Thus, Aim 3 is to test the hypothesis that maternal responsiveness to child negative affect will play a unique role in shaping threat reactivity pathways over time. We hypothesize that emotionally-responsive parenting (assessed with a multi-method protocol) will buffer the associations between IV and threat reactivity profiles and between exposure and symptom trajectories over 1 year. This study will provide critical insight into the etiology of violence-related psychopathology with key implications for developing novel approaches for identification, prevention, and intervention for these highly vulnerable young children.